Field of the Invention
The present disclosure relates to focus detecting apparatuses, and in particular, to a focus detecting apparatus that predicts the motion of a moving object.
Description of the Related Art
Many predicting units for predicting the motion of a moving object have recently been proposed. For example, Japanese Patent Laid-Open No. 2001-21794 discloses a focusing apparatus that stores a plurality of past focus detection results and selects the most suitable function for predicting a change in a future object image-plane position from the results.
It is known in the art that a conversion factor for converting the amount of image displacement (the amount of displacement of two image signals having a parallax) detected in what-is-called imaging-plane phase-difference detection AF (autofocusing using signals acquired by an image sensor) to a defocus amount can have an error. An error in the defocus amount due to the error in the conversion factor causes defocusing. Japanese Patent Laid-Open No. 2010-025997 discloses a technique for correcting the conversion factor by comparing a conversion factor based on the result of the nth focus detection (detection of a defocus amount) and a conversion factor based on the result of the (n−1)th focus detection and assigning a weight.
In predicting the motion of a moving object in imaging-plane phase-difference detection AF, an error in the conversion factor due to vignetting would decrease the prediction accuracy of the motion of the object as compared with a case in which no error occurs. In this case, even if the correction of the conversion factor disclosed in Japanese Patent Laid-Open No. 2010-025997 is applied to a moving object to predict the motion of the object in the optical axis direction, it is sometimes difficult to accurately predict the motion of the object.